The U.S. Environmental Protection Agency (EPA) today released a final toxicity assessment for perfluorobutanesulfonic acid (PFBS). The toxicity assessment can be used along with exposure information and other important considerations to assess potential health risks and determine appropriate actions. According to the assessment, EPA has derived the chronic reference dose of 300 nanograms per kilogram body weight per day (ng/kg-day) based on thyroid function effects. As finalized, it is markedly lower than the draft chronic reference dose from 2018 (10,000 ng/kg-day). The chronic reference dose for perfluorooctanoic acid (PFOA), by comparison, is 20 ng/kg-day. PFBS was included in monitoring under the Third Unregulated Contaminant Monitoring Rule (UCMR) with only eight of 4,920 public water systems detecting levels exceeding the minimum reporting level (MRL) of 90 ng/L. PFBS will also be included under the Fifth UCMR with an MRL of less than 5 ng/L. Water systems should be prepared to respond to potential media inquiries about the potential presence of PFBS in the finished drinking water quality and the corresponding potential health risks. We encourage members to review the following resources: AWWA’s PFAS Resource page Trending in an Instant risk communication guide Source Water Evaluation Guide for PFAS DrinkTap’s PFAS page Questions can be directed to Chris Moody , regulatory technical manager.